Triangle Seminars
Wednesday, 23 Feb 2005
Non-perturbative effects in the c=1 matrix model
📍 London
Sergei Alexandrov
(Utrecht)
Abstract:
I present results on non-perturbative effects in the c=1
string theory. First, I describe a geometric picture found in the CFT
framework which gives an interpretation of D-branes in non-critical
strings in terms of a complex curve associated with any closed string
background. I show that its c=1 limit is degenerate and the degeneracy
can be removed by considering a condensation of tachyon modes. Using
the matrix model description, I calculate the leading as well as the
subleading non-perturbative corrections to the string partition
function. We find them by using the Toda integrable structure and from
the realization of 2D string theory in terms of free fermions. Both
methods give the same result which is also interpreted through
correlation functions of a bosonic field. The leading corrections can
be interpreted in terms of localized D-branes, whereas the sub-leading
ones do not have a simple D-brane description.
I present results on non-perturbative effects in the c=1
string theory. First, I describe a geometric picture found in the CFT
framework which gives an interpretation of D-branes in non-critical
strings in terms of a complex curve associated with any closed string
background. I show that its c=1 limit is degenerate and the degeneracy
can be removed by considering a condensation of tachyon modes. Using
the matrix model description, I calculate the leading as well as the
subleading non-perturbative corrections to the string partition
function. We find them by using the Toda integrable structure and from
the realization of 2D string theory in terms of free fermions. Both
methods give the same result which is also interpreted through
correlation functions of a bosonic field. The leading corrections can
be interpreted in terms of localized D-branes, whereas the sub-leading
ones do not have a simple D-brane description.
Posted by: KCL
Nonperturbative calculations in supersymmetric gauge theories, I
Francesco Fucito
(Rome, Tor Vergata)
Thursday, 24 Feb 2005
Nonperturbative calculations in supersymmetric gauge theories, II
Francesco Fucito
(Rome, Tor Vergata)
The spinorial geometry of supersymmetric backgrounds
Ulf Gran
(King's College)
Abstract:
I will review a recently proposed method for solving the Killing spinor equations in arbitrary dimensions. The efficiency of the method will be illustrated by recent progress on the classification of the supersymmetric solutions of 11D and IIB supergravity.
I will review a recently proposed method for solving the Killing spinor equations in arbitrary dimensions. The efficiency of the method will be illustrated by recent progress on the classification of the supersymmetric solutions of 11D and IIB supergravity.
Posted by: KCL
Friday, 25 Feb 2005
Loop quantum gravity: a view from Lorentz covariant approach
📍 London
Sergei Alexandrov
(Utrecht)
Abstract:
I am going to review the status of loop quantum gravity as it is seen
from the point of view of a Lorentz covariant approach to loop quantization.
I'll start from a brief review of the standard
loop approach based on the SU(2) gauge group, its main results and problems.
Then I'll present another approach which is based on a canonical
formulation of general relativity which is explicitly covariant under
the local Lorentz transformations.
It allows to overcome several problems of the standard loop quantization
and at the same time shows that the latter breaks the diffeomorphism
invariance and is not a correct way for quantizing gravity.
In the covariant framework I'll derive a new spectrum of the area operator,
both for spacelike and timelike surfaces, and show that
its predictions agree with the spin foam quantization.
I am going to review the status of loop quantum gravity as it is seen
from the point of view of a Lorentz covariant approach to loop quantization.
I'll start from a brief review of the standard
loop approach based on the SU(2) gauge group, its main results and problems.
Then I'll present another approach which is based on a canonical
formulation of general relativity which is explicitly covariant under
the local Lorentz transformations.
It allows to overcome several problems of the standard loop quantization
and at the same time shows that the latter breaks the diffeomorphism
invariance and is not a correct way for quantizing gravity.
In the covariant framework I'll derive a new spectrum of the area operator,
both for spacelike and timelike surfaces, and show that
its predictions agree with the spin foam quantization.
Posted by: KCL